Porous inorganic solids have found great utility as catalysts and separation media for industrial applications. These materials are commonly synthesized by using organic cationic templates in the synthesis mixture. The use of surfactants as organic templates provides porous solids with ultra large pores up to 100 Angstroms. The cost of these templating surfactants in many instances represents a major fraction of the overall cost of the molecular sieve. One method of removing the templating surfactants from the pores of the freshly synthesized molecular sieve material is to subject the as-synthesized molecular sieve to high temperatures in a controlled oxygen-containing atmosphere to slowly burn off the residual organic template. This step is commonly referred to in the art of molecular sieve synthesis as calcining. Unfortunately, calcining destroys the templating surfactant. Moreover, the calcined molecular sieve can be more deformed and/or partially collapsed due to shrinkage caused by high calcination temperatures. Inorganic cations may be removed, either before or after calcining, from the as-synthesized molecular sieve by aqueous ion exchange. However, aqueous ion-exchange techniques have proven largely ineffective for removing the organic templating surfactants from layered and other controlled pore synthetic materials. It would, therefore, be highly desirable to provide a method for the removal and recovery of the templating surfactant which would also preserve the integrity of the molecular sieve.
The porous materials in use today can be sorted into three broad categories using the details of their microstructure as a basis for classification. These categories are 1) amorphous and paracrystalline supports, 2) crystalline molecular sieves and 3) modified layered materials, and have been described in detail in U.S. 5 Pat. No. 5,145,816 to Beck, et al., and U.S. Pat. No. 5,143,879 to Whitehurst, which are incorporated by reference as if set forth at length herein.
Zeolites, both natural and synthetic, have been demonstrated in the past to have catalytic properties for various types of hydrocarbon conversion. Certain zeolitic materials are ordered, porous crystalline aluminosilicates having a definite crystalline structure as determined by X-ray diffraction. These crystalline structures contain a large number of smaller cavities which may be interconnected by a number of still smaller channels or pores. These cavities and pores are uniform in size within a specific zeolitic material. Since the dimensions of these pores provide access to molecules of certain dimensions while rejecting those of larger dimensions, these materials are known as "molecular sieves". These molecular sieves have been utilized in a variety of ways in order to take advantage of their properties.
The precise crystalline microstructure of most zeolites manifests itself in a well-defined X-ray diffraction pattern that usually contains many sharp maxima and that serves to uniquely define the material. Similarly, the dimensions of pores in these materials are very regular, due to the precise repetition of the crystalline microstructure. All molecular sieves discovered to date have pore sizes in the microporous range, which is usually quoted as 2 to 20 Angstroms, with the largest reported being about 12 Angstroms.
One particular area of interest involves anchoring or incorporating functional groups into ultra-large pore crystalline materials in order to engineer unique catalytic sites and/or to tailor the pore size as desired. U.S. Pat. No. 5,145,816 to Beck, et al. describes functionalization of ultra-large pore crystalline materials as-synthesized or after removal of the templating surfactant by calcination. It has been found that the structure of calcined ultra-large pore crystalline materials are more deformed and/or partially collapsed due to structure contraction during calcination. As a result, heat calcined ultra-large pore crystalline materials provide fewer silanol groups available for anchoring functionalizing moieties. Moreover, during removal of templating surfactant by calcination the surfactant is burned off, thus being effectively destroyed. On the other hand, the use of uncalcined, surfactant containing ultra-large pore crystalline material is undesirable because expensive templating surfactant is left in the as- synthesized structure of the ultra-large pore crystalline materials. Moreover, some templating surfactants fill the pores of the as-synthesized molecular sieve, and must be removed to provide access to the pores for catalysis or sorption.
U.S. Pat. No. 5,143,879 to Whitehurst teaches a method of recovering organic templates used to synthesize molecular sieves useful as catalysts and sorbents. The method described in the '879 patent requires elevated temperatures, is applied to non-functionalized ultra-large pore crystalline materials and may provide low recovery yields of removed template at room temperature.
Thus, in light of existing technologies for recovery of templating materials and functionalization of synthetic molecular sieves, such as those discussed above, there exists an ongoing need to develop new and useful catalysts and separation media for industrial applications, which are inexpensive and of considerable benefit from the standpoint of processing.
Accordingly, it is an object of the present invention to provide a method for functionalizing ultra-large pore crystalline material concurrently with recovery of is high yields of templating surfactant.